The invention relates to a new medical use for compounds which act as antagonists of 5-hydroxytryptamine (5-HT) at 5HT3 receptors.
5-HT3 receptor antagonists may be identified by methods well known in the art, for example by their ability to inhibit 3-(5-methyl-1H-imidazoie4-yl)-1-[1-[3H]-methyl-1H-indol-3-yl]-1-propanone binding in rat entorhinal cortex homogenates (following the general procedure described by G Kilpatrick et al, Nature, 1987, 330, 746-748), and/or by their effect on the 5-HT-induced Bezold-Jarisch (B-J) reflex in the cat (following the general method described by A Butler et al, Br. J. Pharmacol., 94, 397-412 (1988)).
A number of different 5-HT3 receptor antagonists have been disclosed, for example those of group A: indisetron, Ro-93777, YM-114, granisetron, talipexole, azasetron, tropisetron, mirtazapine, ramosetron, ondansetron, lerisetron, alosetron, N-3389, zacopride, cilansetron, E-3620, lintopride, KAE-393, itasetron, mosapride and dolasetron.
In UK Patent No. 2209335, incorporated herein by reference, there is disclosed, inter alia, the compound 2,3,4,5-tetrahydro-5-methyl-2-[(5-methyl-1 H-imidazol-4-yl)methyl]-1H-pyrido[4,3-b]indol-1-one, now known as alosetron, which may be represented by the formula (I): 
and pharmaceutically acceptable salts, solvates and pharmaceutically acceptable equivalents thereof, in particular its hydrochloride salt.
5-HT3 receptor antagonists are known to be useful in the treatment of a variety of conditions involving 5-HT3 receptor-mediated mechanisms, including in particular emesis.
Irritable bowel syndrome (IBS) is the most common diagnosis made by gastroenterologists (1) and is characterised by abdominal pain and discomfort and altered bowel functions (2-4). To date, no laboratory or structural defects have been identified in IBS and the formal diagnosis is based upon a constellation of symptoms defined by either the Manning (5) or Rome Criteria (6).
The current understanding of the pathophysiology or aetiology of IBS is limited, and no proven effective therapy is available (3,7). Moreover, many patients gain slight or even no relief from such therapies. Thus, there is a real need to develop new medicines for the treatment of IBS.
Over the last two decades compelling evidence has accumulated that a state of enhanced perception of visceral stimuli develops in patients with IBS (2,3,8-10). In balloon distension studies of the colon or rectum the threshold for sensation of pain is lower in IBS patients compared to controls, and this has been proposed as a biological marker for IBS (11). In view of the evidence for enhanced visceral perception in IBS and the frequent occurrence of pain, any agent considered to be of utility in the treatment of IBS should demonstrate effectiveness in the relief of pain.
Of the classes of therapeutic agents which have been proposed for the treatment of abdominal pain in IBS, 5-HT3 receptor antagonists are among the most promising. In animal models, these agents have been shown to decrease visceral pain responses (12,13). Furthermore, the 5-HT3 receptor antagonist, ondansetron, has been shown to slow colonic transit in normal volunteers (14-15). In patients with IBS ondansetron increases rectal compliance (16) and in diarrhoea-predominant IBS patients ondansetron improves stool consistency (17-19). Ondansetron also inhibits the contractile response of the colon in healthy volunteers in the early postprandial period (20), the time when many IBS patients experience symptoms. A second 5-HT3 receptor antagonist, granisetron, has also been shown to produce a decrease in rectal sensitivity, and reduce post-prandial motor activity in IBS patients (21).
Alosetron is a potent and selective 5-HT3 receptor antagonist, and in preliminary reports, alosetron has been shown to improve abdominal pain (22), and to slow colonic transit in IBS patients (23).
Surprisingly, it has now been found that 5-HT3 receptor antagonists represent a particularly effective and well tolerated therapy in nonconstipated female IBS patients.
According to one aspect the invention therefore provides a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof for use in the treatment of nonconstipated female IBS.
In one preferred aspect the invention provides a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof for use in the treatment of diarrhoea predominant female IBS.
In another preferred aspect the invention provides a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof for use in the treatment of alternating constipation/diarrhoea IBS.
By pharmaceutically acceptable derivative is meant any pharmaceutically acceptable salt or solvate of a 5-HT3 receptor antagonist or any other compound, which upon administration to the recipient is capable of providing (directly or indirectly) a 5-HT3 receptor antagonist or an active metabolite or residue thereof.
In one preferred aspect the invention provides a compound of Group A or a pharmaceutically acceptable derivative thereof for use in the treatment of nonconstipated female IBS.
In a further preferred aspect the invention therefore provides alosetron or a pharmaceutically acceptable derivative thereof for use in the treatment of nonconstipated female IBS.
Suitable pharmaceutically acceptable salts of alosetron include acid addition salts formed with inorganic or organic acids (for example hydrochlorides, hydrobromides, sulphates, phosphates, benzoates, naphthoates, hydroxynaphthoates, p-toluenesulphonates, methanesulphonates, sulphamates, ascorbates, tartrates, salicylates, succinates, lactates, glutarates, glutaconates, acetates, tricarballylates, citrates, fumarates and maleates), and solvates (for example hydrates) thereof.
In a preferred embodiment of the present invention alosetron is employed in the form of its hydrochloride.
In another aspect, the invention provides the use of a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof in the manufacture of a medicament for the treatment of nonconstipated female IBS.
In another aspect, the invention provides a method of treatment of nonconstipated female IBS which comprises administering an effective amount of a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof.
Within the above aspects and preferred aspects of the invention, the use of a 5-HT3 receptor antagonist of Group A, more preferably alosetron, is especially preferred.
It is to be understood that reference to treatment includes both treatment of established symptoms and prophylactic treatment, unless explicitly stated otherwise.
Conveniently, a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof may be formulated in conventional manner using one or more pharmaceutically acceptable carriers or excipients. Thus a 5-HT3 receptor antagonist or a pharmaceutically acceptable derivative thereof may, for example, be formulated for oral, sub-lingual, buccal, parenteral, rectal or intranasal administration, or in a form suitable for administration by inhalation or insufflation (either through the mouth or nose), or in a form suitable for topical administration.
For oral administration the pharmaceutical compositions may take the form of, for example, tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents (e.g. pregelatinised maize starch, polyvinylpyrrolidone or hydroxypropyl methylcellulose); fillers (e.g. lactose, microcrystalline cellulose or calcium phosphate); lubricants (e.g. magnesium stearate, talc or silica); disintegrates (e.g. potato starch or sodium starch glycollate); or wetting agents (e.g. sodium lauryl sulphate). The tablets may be coated by methods well known in the art. Liquid preparations for oral administration may take the form of, for example, solutions, syrups or suspensions, or they may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may be prepared by conventional means with pharmaceutically acceptable additives such as suspending agents (e.g. sorbitol syrup, methyl cellulose or hydrogenated edible fats); emulsifying agents (e.g. lecithin or acacia); non-aqueous vehicles (e.g. almond oil, oily esters or ethyl alcohol); and preservatives (e.g. methyl or propyl-p-hydroxybenzoates or sorbic acid).
For buccal administration the compositions may take the form of tablets or lozenges formulated in conventional manner.
For parenteral administration the compositions may take the form of injections, conveniently intravenous, intramuscular or subcutaneous injections, for example bolus injections or continuous intravenous infusions. Formulations for injection may be presented in unit dosage form e.g. in ampoules or in multi-dose containers, optionally with an added preservative.
The compositions for parenteral administration may take such forms as suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilising and/or dispersing agents. Alternatively, the compositions may be in dry form such as a powder, crystalline or freeze-dried solid for constitution with a suitable vehicle, e.g. sterile pyrogen-free water or isotonic saline before use. They may be presented, for example, in sterile ampoules or vials.
For rectal administration the compositions may take the form of suppositories or retention enemas.
Tablets for sub-lingual administration may be formulated in a conventional manner.
For intranasal administration, or administration by inhalation or insufflation, conventional formulations may be employed.
For topical administration the pharmaceutical compositions may be liquids, for example solutions, suspensions or emulsions presented in the form of creams or gels.
In addition to the formulations described previously, the compositions may also be formulated as a depot preparations. Such long acting formulations may be administered by implantation (for example subcutaneously, transcutaneously or intramuscularly) or by intramuscular injection. Thus, for example, the compositions may be formulated with suitable polymeric or hydrophobic materials (for example as an emulsion in an acceptable oil) or ion exchange resins, or as sparingly soluble derivatives, for example, as a sparingly soluble salt.
It will be appreciated that the precise therapeutic dose of a 5-HT3 receptor antagonist, expressed in the form of its free base, will depend on the age and condition of the patient and the nature of the IBS to be treated, and will be at the ultimate discretion of the attendant physician.
However, in general, effective doses for the treatment of nonconstipated female IBS patients will lie in the range of 0.001 to 500 mg, such as 0.01 to 100 mg, preferably 0.05 to 50 mg, for example 0.5 to 25 mg per unit dose, which could be administered in single or divided doses, for example, 1 to 4 times per day.
In a preferred embodiment, effective doses of alosetron for the treatment of nonconstipated female IBS patients will lie in the range of 0.01 to 100 mg, such as 0.05 to 50 mg, preferably 0.1 to 25 mg, for example 0.5, 1, 2 or 4 mg of alosetron per unit dose, which could be administered in single or divided doses, for example, 1 to 4 times per day.